KR20010077855A - Material of positive plate for lithium secondary cell and lithium secondary cell - Google Patents

Abstract

A substance represented _{by the} general formula Li _{1 + x} Mn _2-x O _{4 + y} (0 ≦ _x ≦ 0.08, −0.05 ≦ _y ≦ 0.02), wherein the total Mn average oxidation number M of the substance is 3.540 or more and 3.560 or less, The positive electrode material for lithium secondary batteries whose Mn average oxidation number m of the finishing 5 weight% component satisfy | fills M-0.02 <= m <= M, and the lithium secondary battery using the same, The positive electrode for lithium secondary batteries ) LiMn ₂ O ₄ spinel compound is used as a material to maintain a good initial capacity and to find the relationship between the Mn valence (oxidized water) and the cycle characteristics of the material, thus providing a high filling rate. The positive electrode material for lithium secondary batteries which has favorable charging cycle characteristics which hold | maintains densification can be obtained.

Description

Positive electrode material for lithium secondary battery and lithium secondary battery {MATERIAL OF POSITIVE PLATE FOR LITHIUM SECONDARY CELL AND LITHIUM SECONDARY CELL}

Lithium secondary batteries have a higher energy density than conventional secondary batteries, and thus are widely used as batteries for electronic devices, such as mobile phones, portable video cameras, and notebook computers. The use as a distributed batch type power supply is expected, and the research and development for obtaining high capacity and high efficiency battery are actively performed.

LiCoO ₂ is currently used as a positive electrode active material for lithium secondary batteries on the market, but due to its poor thermal stability, there is a problem in safety, and it is also possible to mine earth resources of cobalt itself. It has the disadvantage of low reserves and high price.

For this reason, researches on lithium-nickel composite oxides having abundant resources and excellent economical efficiency have been conducted in place of the above. However, this lithium-nickel composite oxide has a process difficulty in that oxygen airflow is required when synthesizing LiNiO ₂ , and a part of Ni is originally incorporated into a site where Li should enter. The current situation is that it is practically not used because there is a drawback that there is a disorder of (i) and sufficient cycle characteristics cannot be obtained.

For these reasons, LiMn ₂ O ₄ spinel compounds, which are cheaper than cobalt or nickel and rich in reserves, have attracted attention and recent studies have been actively conducted. Therefore, it is expected that it can be used in the future as the electric vehicle as described above.

Spinel LiMn ₂ O ₄ , which is a lithium-manganese composite oxide, has Li at an 8a tetrahedral site and Mn at a 16d octahedral site. The arrangement of oxygen is a cubic fine-charged structure, and the basic skeleton is λ-MnO ₂ . Since lithium ions reversibly occupy tetrahedral sites, structural destruction of the basic skeleton hardly occurs in a lithium secondary battery using LiMn ₂ O ₄ as a positive electrode material. Charging and discharging only cause expansion and contraction of crystal lattice. For this reason, charging and discharging are stable.

By the way, although the LiMn ₂ O ₄ spinel compound has high thermal stability in this manner, the secondary battery using this as a positive electrode active material has poor cycle characteristics, which causes great practical problems.

Conventionally, in order to remedy these drawbacks, it is possible to improve the cycle characteristics by increasing the uniformity of the active material or by doping other materials, but it is still sufficient. There is no number.

The present invention relates to a positive electrode (+: positive electrode) material for a lithium secondary battery that can maintain a good initial capacity and has excellent charging characteristics.

1 is a schematic cross-sectional view of a coin cell for battery characteristic evaluation.

(Initiation of invention)

The present invention uses a LiMn ₂ O ₄ spinel compound as a positive electrode material for a lithium secondary battery to maintain a good initial capacity, and at the same time, the Mn valence (“oxidized water”) of this material is the same. ) And the cycle characteristics, and to establish a positive electrode material for a lithium secondary battery and a lithium secondary battery using the same having good charge cycle characteristics maintaining a high charge rate.

The present invention is based on what has been found above,

1. A substance represented by the general formula Li _{1 + x} Mn _2-x O _{4 + y} (0 ≦ _x ≦ 0.08, −0.05 ≦ _y ≦ 0.02), wherein the total Mn average oxidation number M of the substance is 3.540 or more, 3.560 The positive electrode material for lithium secondary batteries whose Mn average oxidation number m of the 5 weight% component below is satisfied with M-0.02 <= m <= M.

2. Lithium secondary battery which has positive electrode material for lithium secondary battery as described in said 1

, To provide.

(Embodiment of invention)

Currently, the LiMn ₂ O ₄ spinel compound used in the lithium secondary battery is a solid-phase reaction in which a mixture of heat-treated lithium salt and manganese salt is heat-treated at a practical level, except for a special case at the laboratory level. The law is being used.

The solid phase reaction proceeds with the main reaction of the interdiffusion between lithium in lithium salts and manganese in manganese salts. In this case, it is ideal to diffuse uniformly with each other, but the lithium salt is thermally unstable and easily decomposed, and in fact, the reaction proceeds in the form of lithium diffusion in the manganese salt.

LiMn ₂ O ₄ spinel compound synthesized through this reaction mode has a certain particle size distribution of the manganese salt powder of the raw material, so a difference in lithium concentration occurs for each particle.

To explain this in more detail, for example, the larger the particles of manganese salt powder, even if lithium does not diffuse to the center, the smaller the particle size, the diffusion of lithium proceeds to the center, and depending on the size of the particles of the powder Differences occur in diffusion concentrations, resulting in concentration gaps.

As described above, when the cycle characteristics of the battery were examined as they contained the difference in lithium concentration between particles, the first cycle reaction, together with charge and discharge, exhibited good load characteristics at high voltage peculiar to the spinel. Although shown after the 2nd cycle, deterioration of charge and discharge capacity is shown.

On the other hand, it is well known that LiMn ₂ O ₄ , which has a Mn valence of less than 3.5, has a remarkably bad cycle characteristic. As described above, when synthesized in a solid phase reaction, the gap between the particles cannot be avoided, and in the total average, even if the Mn valence is 3.5 or more, when the Li concentration is lowered, the Mn valence ( The probability that particles containing crystallites of less than 3.5 are produced increases, which is considered to be a cause of poor cycle characteristics.

In order to solve the above problems, the present invention aims to control the gap between the Mn valences.

Control of the Mn valence gap can be controlled mainly by the Li / Mn ratio, but when a high initial capacity is desired, Li is reduced and Mn valence is possible to 3.5. You need to be as close as possible.

That is, when high capacity is desired, it is necessary to make the gap of Mn valence small as much as possible, and to reduce the probability of crystallite and particle | grains of 3.5 or less. In the case of synthesizing by the solid phase method, it is necessary to minimize the particle size distribution first because the gap between the valences mainly depends on the distribution of particle diameters.

In addition to the distribution, the presence of particles having a large particle size has an upper limit in particle size because the contact area with a lithium source is biased to one side and causes a large gap in the particles. That is, of course, the refinement and homogenization of raw material powder are also necessary.

From the foregoing, the substance represented by the general formula Li _{1 + x} Mn _2-x O _{4 + y} (0 ≦ _x ≦ 0.08, −0.05 ≦ _y ≦ 0.02), wherein the total Mn average oxidation number M of the substance is 3.540 or more, 3.560 Below, it is necessary for Mn average oxidation number m of the finishing 5 weight% component to satisfy M-0.02 <= m <= M.

If y is less than -0.05, LiMnO ₂ is produced, and it is difficult to obtain a spinel single phase. In addition, when y exceeds 0.02, LiMnO ₂ or Li ₂ MnO ₃ is produced depending on the conditions, and it is difficult to obtain a spinel single phase, and at the same time, adversely affects the cycle characteristics.

The positive electrode material for lithium secondary batteries of the present invention was found to significantly improve the cycle characteristics by using LiMn ₂ O ₄ as the positive electrode active material.

In order to obtain LiMn ₂ O ₄ , electro-synthesis or chemical synthetic manganese oxide is used to carry out quartet classification to remove particles having a predetermined particle size or more. Although the smaller one of the classification point at this time is preferable, about 25 micrometers is industrially considered to be a limit. The finishing component is pulverized by pneumatic or mechanical pulverization, and then mixed with a lithium salt by performing a particle size aid so that the average particle diameter becomes 3 탆 to 12 탆. In addition, the lower and lower part which passed the sieve component is similarly mixed with a lithium salt.

This can be obtained by heat treatment using a heating apparatus such as an electric furnace between 650 ° C and 900 ° C in an inert atmosphere, in the air, or in an oxidizing atmosphere. The mean particle size at this time is largely dependent on the grinding conditions of the particle size, classification point, and finishing component of manganese oxide as a starting material. desirable.

When the average particle diameter is less than 3 µm, agglomeration of the powder appears, and the powder stays in the crushing device after the synthesis or in the transport copper. It is not preferable because industrial problems such as i) occur. On the other hand, when the average particle diameter is adjusted to 20 µm or more, it is necessary to set the classification point to at least 50 µm or more, and to suppress the particle size distribution to reduce the gap between Mn valences. It is against the point.

Hereinafter, although it demonstrates according to an Example, these are only the examples presented in order to make understanding easy, and this invention is not limited to these Examples. Therefore, various modifications are included in the range which does not deviate from the summary of this invention.

In the practice of the present invention, battery characteristics were evaluated using the coin cell shown in FIG. This coin-type cell mixes polyvinylidene fluoride and n-methylpyrrolidone as a conductive carbon, a binder, and a positive electrode active material, and uses a doctor blade method. What was formed into a film on the SUS board 4 was made into the positive electrode 8.

Upper and lower lids made of SUS, using an EC / DEC solution containing a metal lithium plate as a separator 7 and a negative electrode 6 and 1M LiPF ₆ as an electrolyte 5 as a supporting salt. It was enclosed by the gasket 2 made of l, 3, and Teflon.

By this cell, battery capacity and cycle characteristics were evaluated as battery performance.

(Examples 1-2 and Comparative Examples 1-3)

In Example 1, the average value M of the total Mn average oxidation number is 3.547, the Mn average oxidation number m of the finishing 5 wt% component is 3.535, and the tap density is 2.0 g / cc.

The charge capacity after 80 cycles of this Example 1 is 115 mAh / g (capacity retention after 80 cycles is 95%), and the charge cycle characteristics at room temperature are excellent.

The above result is shown in Table 1 with another Example and a comparative example.

In Example 2, the average value M of the total Mn valences adjusted by the classification method was 3.557, and the average value M of the Mn valences m of the finishing 5 weight% component was 3.550. to be. The tap density is also 2.2 g / cc.

As evident in this example, the charge capacity after 80 cycles becomes 114 mAh / g (the capacity retention after 80 cycles is 96%) by suppressing the gap between Mn valences, indicating good charge cycle characteristics.

In comparison, Comparative Examples 1, 2, and 3 each had a total Mn average oxidation number M of 3.536,

3.545 and 3.588, Mn valence m of the finishing 5 weight% component is 3.518, 3.520, and 3.572, respectively.

As is evident from these, in Comparative Example 1, although the Mn valence m of the 5 wt% component of the present invention is within the scope of the present invention, the average value M of the total Mn valences of the present invention is Smaller than range In Comparative Example 2, the average M of all Mn valences is within the scope of the present invention, but the Mn valence m of the finishing 5 wt% component is smaller than the range of the present invention. Moreover, although the Mn valence m of the finishing 5 weight% component is in the scope of this invention, the comparative example 3 has the average value M of all Mn valences exceeding the range of this invention.

As a result, the discharge capacities after 80 cycles were 106 mAh / g, 102 mAh / g and 100 mAh / g, respectively (capacity retention after 80 cycles was 85%, 84% and 92%, respectively). None was bad (in particular, Comparative Example 3 had a low initial discharge capacity of 109 mAh / g).

The average values of the Mn valences of the substances represented by the general formula Li _{l + x} Mn _2-x O _{4 + y} (0 ≦ _x ≦ 0.08, −0.05 ≦ _y ≦ 0.02) are 3.540 or more and 3.560 or less, It was confirmed that the filling cycle characteristic was excellent in the range where Mn average valence m within 5 weight% is smaller than M-0.02 <= m <= M from the smaller the mapping number.

Any deviation from the range of Mn average valences described above resulted in poor cycle characteristics.

Table 1

Mn singular m with 5% by weight of component Mn Mean Oxidation Number M Initial discharge capacity (mAh / g) Discharge capacity after 80 cycles (mAh / g) Capacity maintenance rate after 80 cycles Tap Density (g / cc) Example 1 3.535 3.547 121 115 95% 2.0 Example 2 3.550 3.557 119 114 96% 2.2 Comparative Example 1 3.518 3.536 125 106 85% 2.2 Comparative Example 2 3.520 3.545 121 102 84% 2.3 Comparative Example 3 3.572 3.588 109 100 92% 2.3

The present invention uses a LiMn ₂ O ₄ spinel compound as a positive electrode material for a lithium secondary battery to reduce the gap of Mn valence and to make contact with conductive carbon. By improving and grain boundary control, initial stage capacity | capacitance can be maintained favorable and charging efficiency can be raised remarkably.

Claims (2)

A substance represented _{by the} general formula Li _{1 + x} Mn _2-x O _{4 + y} (0 ≦ _x ≦ 0.08, −0.05 ≦ _y ≦ 0.02), wherein the total Mn average oxidation number M of the substance is 3.540 or more and 3.560 or less, The positive electrode material for lithium secondary batteries whose Mn average oxidation number m of the finishing 5 weight% component satisfy | fills M-0.02 <= m <= M. It has a positive electrode material for lithium secondary batteries of Claim 1, The lithium secondary battery characterized by the above-mentioned.